Strip line hybrid ring



Jan. 5, 1965 J. R. DENT 3,164,791

STRIP LINE HYBRID RING Filed May 5. 1961 2 Sheets-Sheet 1 Fae-.2

nnnnn m INVENTOR.

JoHN 2. DENT BYXAF I ATTORNEYS:

1965 J. R. DENT 3,164,791

STRIP LINE HYBRID RING Filed May 5. 1961 2 Sheets-Sheet 2 INVENTOR Joan E. DENT ATTORNEYS STRW LINE HYBRID RING John R. Dent, Falls Church, Va., assignor to Melpar, Inc,

Falls Church, Va, a corporation of Delaware Filed May 5, 1961, Ser. No. 125,601 2 Claims. (Cl. 333-11) lThe present invention. relates generally to electronic directional couplers and more particularly to a coupler that is compact, light-weight, easy to manufacture and which provides small losses between oneterminal and a common terminal or between a secondterminal and the common terminal but which provides high losses over a fairly wide frequency band between the first and second terminals.

' Prior directional couplers have frequently proven undesirable for many applications because of their relatively largesize and weight. To a certain extent, this has been as a result of the external termination that is necessary and because of the necessity for a 1.5 wave length circular loop. Also, prior art directional couplers have proven inadequate for many purposes because of highly critical dimensions, causing substantial increased production cost. If the dimensions of the prior art devices are not critically maintained, frequently a great deal of attenuation in the forward, as well as reverse direction, results and the .eifectiveness of the device is accordingly reduced.

Accordingly, it is an object of the present invention to provide a new and improved directional coupler.

It is a further object of the present invention to provide a directional coupler that may be packaged in a compact, light-weight unit that does not require external terminations and as a result is Well suited for airborne and missiles application.

It is another object of the present invention to provide an electronic directional coupler that is inexpensive to manufacture due to a lack of criticality in its dimensions and which exhibits substantially no attenuation in the forward direction and great attenuation in the backward direction over a fairly wide frequency band.

Briefly, the present invention employs a circular strip line element mounted on a dielectric board. The circular element contains three tabs or terminals, two located in proximity to each other and each a quarter wave length from a third tab located on the opposite side of the circle'. The strip line conductor between one of the adjacent tabs and the third tab is essentially a quarter wave length transmission line. The segment of the strip line conductor between the two adjacent tabs is removed and a resistor is inserted in a slot in the dielectric board where the segment was removed.

The half wave length between the two adjacent tabs. results in a 180 phase shift of the propagated energy between them. A resistor is connected between the two adjacent tabs so that cancellation of the 180 phase shifted signal and the original signal is effected. The value of the resistor is chosen so that the power supplied to the tab is divided equally between it and the transmission line.

If asignal is supplied to the remote or third tab, equal voltages are produced at the adjacent tabs. Any re-- flected energy from the load connected to one of the adjacent tabs is not reflected back to the other adjacent tab but is reflected to the third. Since the transmission 3 United States Patent M 3,164,791 Patented Jan. 5, 1965 ice line between one adjacent tab and the third tab is a quartabs, resulting in an output signal at the third tab, virtually no energy interchange between the signals supplied to the adjacent tabs results. This device may also be modified to include any desired number of adjacent tabs.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 of the drawings is a schematic illustration of one embodiment of the present invention;

FIGURE 2 is a schematic illustration of an additional embodiment of the present invention;

FIGURE 3 is an exploded illustration of one embodiment of the actual apparatus according to FIG- URE 1;

FIGURE 4 is a side sectional view of the assembled apparatus of FIGURE 3; and

FIGURE 5 is an exploded illustration of another embodiment of the apparatus according to FIGURE 1.

The schematic diagram, FIGURE 1, of one embodiment of the present invention, discloses a substantially circular metal ring 11 having two adjacent tabs 12, 13, and a remote or third tab 14. The segment of the circle between tabs 12 and 13 is removed and resistor 10 is connected therein. The total distance between points 15 and 16 on the circular element 11, respectively adjacent to tabs 12 and 13, is approximately equal to one-half wave length of the signal which it is expected will be fed to the coupler. Since point 17 on the circular element 11, directly adjacent to tab 14, is approximately one half the distance between points 15 and 16 it is seen that arms 18 and 19 of metal ring 11 are approximately a quarter wave length long. Thus, arms 18 and 19 are effectively quarter wave length transmission lines and serve to provide a, 9 0 phase shift for the signals at tabs 12, 13 and 14 In use, a signal source may be connected to tab 14 with equal output voltages being supplied to points 15 and 16 and consequently to tabs 12 and 13. Any signal that may be reflected from the load connected to either tab 12 or 13 is not reflected around to the other adjacent tab.

Thus, if a signal is reflected back from the load connected to tab 12, the energy therefrom does not appear at tab 13 but is only reflected to tab 14. Likewise, any energy reflected from the load connected to tab 13 back to the circular element 11 does not appear in the device connected to tab 12.

Signal sources may also be connected to tabs 12 and 13 with a resultant combined output signal being obtained from the load connected to tab 14. The independent signal supplied to tab 13 does not appear in the signal coupled to tab 12 and conversely the signal coupled to of frequency corresponding to that for the coupler legs 18 and 19 is connected to tab 14. If the loads connected to tabs 12 and 13 match the transmission lines 18 and 19, to which they are respectively connected, no reflections appear at points 15 and 16, consequently the voltages at these points are of equal magnitude and phase. As a result, tabs 12 and 13 supply no energy to the transmission lines 18 and 19 and no energy is dissipated in resistor 10, connected between points 15 and 16. However, if there is a mismatch between one of the loads connected to tabs 12 and 13 and lines 18 and 19, reflections are produced at points 15 and 16 and energy is supplied back to the respective transmission line. To provide for isolation between points 15 and 16 for the reflected energy at either of them, two paths are provided, one through resistor and the other by Way of legs 18 and 19, which together constitute a half wave length transmission line. The half wave length transmission line inverts the reflected signal at terminal 15. If resistor 10 is chosen to absorb the same amount of power from point as point 15 supplies to the transmission lines, the voltage at point 16, due to reflected energy at point 15, is zero due to cancellation of the inverted voltage and the voltage supplied through resistor 10.

The value of resistor 10 can be chosen to produce a voltage null at point 16 with regard to the reflected signal at the point 15. As a consequence, the impedance at point 16 is zero with regard to the reflected signal at point 15 and no power is supplied to point 16 by the reflected signal from point 15. Thus, equal amounts of reflected power from point 15 are supplied to resistor 10 and tab 14, the tab being supplied via line 18. If the impedances of the devies connected to tabs 12 and 13 are equal, it can be shown the value of resistor 10 must equal twice the impedance of one device. Thus, resistor 10 may be considered a pair of series resistors, one resistor connected to tab 12 and another connected to tab 13, each resistor being approximately equal to the impedance of the device connected to its respective tab. If the devices connected to tabs 13 and 14 are both resistive loads, each having an impedance of 50 ohms, resistor 10 should equal 100 ohms.

While the foregoing description was made with regard to a signal applied to tab 14 it is to be understood that it applies equally to signals coupled directly to tabs 12 and 13. Signals applied directly to tabs 12 and 13 have the same effect as the signal which would be reflected from a load. Also it is apparent that energy supplied to point 16, either from a signal source connected to tab 13 or from reflected load energy, results in an identical mode of operation as that for energy supplied to point 15 by tab 12.

It is to be understood that the length of arms 18 and 19 is not limited to a quarter wave length but may be any odd multiple of a quarter wave length, that is (2n1))\/ 4, where it is the wave length of the signal supplied to the coupler and n is any integer. It is necessary only that legs 18 and 19 elfectively introduce a 90 phase shift to the signals fed thereto from points 15 and 16 and that they be of a characteristic impedance to effect matching as closely as possible.

FIGURE 2 of the drawings discloses another embodiment of the present invention where three remote tabs are decoupled. This embodiment comprises a substantially circular metal member 21 having two outer legs 22 and 23 and a center leg 24, each leg being quarter wave length long. One end of each leg is connected at point 25 to common tab 26. Tabs 27, 28, 29 respectively connected to legs 22, 23 and 24 serve to connect the other ends of the respective legs to external signal sources or loads. The other ends of each of the legs are connected together by a star connected resistor network, so resistor 31 is connected between the end of leg 22 and common point 32, resistor 33 is connected between the end of leg 23 and point 32 while resistor 34 is connected 4 between the end of leg 24 and point 32. It is understood the length of a leg is construed as the distance between point 25 and the resistor connection point and there is no ground connection to common point 32.

In operation, if it is assumed that a signal is supplied to tab 26 by a microwave source and there is an impedance match of the devices connected to tabs 27, 28 and 29, the voltages at the ends of legs 22, 23 and 24, where the resistances are connected, are of equal phase and magnitude. Thus, as in the case of the structure disclosed in FIGURE 1, no reflections occur and no power is dissipated in resistors 31, 32 and 33. If there is a load reflection at the end of one of the legs, or if one of the tabs 27, 28 or 29 is connected to a signal source, the reflected or source of energy is absorbed in the resistor network and the impedance connected to tab 26.

The structure illustrated in FIGURE 2 operates similarly to that of FIGURE 1. If it is assumed there is energy being supplied by tab 27 into the coupler either as a result of reflected energy or because of a signal source, the energy is fed to the quarter wave length leg 22 and to resistor 31. The voltage supplied to leg 22 is fed to the end of leg 23 by two paths, one path being established by quarter wave length legs 22 and 23 and the other being established by resistors 31 and 33. Because legs 22 and 23 together are a half wave length transmission line, the signal arriving at the end of leg 23 is inverted with respect to the signal starting from the end of leg 22. To obtain a voltage null at tab 28 from the signal supplied by tab 27 resistors 31, 33- and 34 are designed to absorb /a the power of the signal supplied by tab 27, thereby feeding Ma the power of this signal to leg 22 and the device connected to tab 26. In general, it is seen that the resistance network absorbs of the power from one of the tabs and of the power is supplied to the transmission line and the device connected to the common tab, where N is the number of transmission lines.

The signal supplied through tab 27 to the coupler is nulled at the end of leg 24 closest to tab 29 due to the paths established by means of resistors 31 and 34 and legs 22 and 24. Since the voltage supplied to the ends of legs 23 and 24 from leg 22 is zero, it is apparent that the power supplied to the ends of these legs from leg 22 is zero. Consequently, the power which tab 27 feeds to the coupler is distributed between resistors 31, 33 and 34 and the device connected to tab 26 via leg 22. It should thus be apparent that isolation of the signal at tab 28 relative to tabs 27 and 29 is accomplished in a similar manner. Also isolation occurs for the same reason between the energy at tab 29 relative to tabs 27 and 28.

If the devices (either signal or load) connected to tabs 27, 28 and 29 have the same impedance, it can be shown that each of the resistors 31, 33 and 34 should be equal to the impedance of one of the devices so the series circuit between any of these tabs is twice the impedance of one device.

It is possible to construct a directional coupler having as many arms as desired with the approach utilized in FIGURES 1 and 2. Thus, if it is desired to supply one signal to N separate loads and to provide isolation between the sources it is necessary only to provide N different quarter wave length transmission line legs between the source and the various loads. It is necessary only to connect the proper value resistor between the opposite ends of the transmission line legs in order to perfect zero power transfer from one leg to the other.

FIGURE 3 discloses an exploded view of the directional coupler 11 schematically illustrated in FIGURE 1 and comprises a copper clad fiber glass dielectric board 41 upon which the ring 11 is mounted in a strip line manner. In order to effect mechanical rigidity, a second metallic ring of identical shape and construction to ring 11 is placed on the opposite side of dielectric board 41 and in register with ring 11. A slot 42 is machined in the board between the opposite ends of legs 18 and 19 in which a micro-wave resistor, of the evaporated film type, is inserted.

Board 41 and ring 11, which'it carries, are maintained in place within U-shaped, metal bracket 43 by means of bolts that are suitably placed within the bores of bracket bars 44 and 45. Bracket bar 44 is secured in place within U-shaped metal bracket 43 by means of screws 46 and 47 which fit through the bores in bracket 43 into suitable bores within bar 44. Thus, bar 44 serves as a ledge on the base of bracket 43. Bar 45 is secured within bracket 43 by means of screw 48 which extends through a suitable bore in one of the legs of bracket 43 and into the bore provided in the end of bar 45. Another screw, not shown, similar to screw 48 fits through a bore provided in the other leg of bracket 43 and into a bore at the other end of bar 45.

Micro-wave connectors 51, 52 and 53 are connected to the various tabs on the directional coupler 11 by means of bores 54, 55 and 56 provided therefor on the legs of bracket 43. These connectors are mechanically maintained in place by means of any suitable means, such as screws, which engage the threaded bores provided on the legs of bracket 43. Leads 57 and 58 of connectors 51 and 52 are soldered to tabs 12 and 13 of coupler 11 on both sides of the board 41. Similarly, the leads within connector 53 are connected to tabs 14. The exterior portions of connectors 51, 52 and 53 are electrically connected to the bracket 43 to provide a ground for the signals coupled by the connectors to the coupler.

Ground shield 61, comprising two substantially fiat rectangular plates joined together at one edge to form a U- shaped metallic member, is inserted within bracket 43 so that the edges of the legs of member 61 engage the base of bracket 43. Member 61 is secured to bracket 43 by means of screws 62 and 63 which extend through the bores provided near the end of each of its legs and through the bores in board 41 and ledge 44. Member 61 is secured in place by means of nuts that are threaded onto bolts 62 and 63.

FIGURE 4 discloses a side elevation, in section, of the assembled mechanical structure of FIGURE 3. From this figure, it is seen that the base of bracket 43 maintains grounding plate 61 and dielectric board 41 in place by means of screw 47, threaded into ledge 44. Also, the arrangement of bolt 63 through the bores in the legs of ground plate 61 and dielectric board 41 is clearly illustrated. A spacer 64 is provided between one leg of member 61 and dielectric board 41 to maintain rigidity. Bolt 65 is threaded through a bore provided in the upper portion of one leg of ground plate 61 and extends through a bore within rod 45 and a bore in dielectric board 41.

It is necessary that the width of tabs 12, 13 and 14 be less than the diameter of bores 54, 55 and 56 with which they are associated so no short circuiting of the signals coupled to these tabs to ground results. The width of the tabs is determined by ground plane spacing from the strip line, dielectric constant of the propagating medium, their own thickness and the impedance of the device which is connected thereto.

FIGURE 5 is an exploded diagram of another possible physical arrangement for the present invention. Dielectric board 41, containing stripline element 11 and slot 42 for receiving resistor 10, is constructed substantially the same as in the embodiment of FIGURES 3 and 4. Board 41 is positioned on ledges 71 and 72, interiorly of substantially U-shaped block 73. Legs 74 and 75 of an additional substantially U-shaped block 76 sit on upright legs 77 and 78, respectively, of block 72. The widths of legs 74 and 75 are approximately equal to that of legs 77 and 78 plus the width of ledges 71 and 72, respectively, to hold board 41 securely in place. Blocks 73 and 76 are secured together by screws 81-84 inserted in the bores drilled in both blocks. The screws may be secured by threading the bores in block 73 or with suitable bolts. Metallic blocks 73 and 76 are substantially U-shaped so the air between the legs thereof serves as insulation between the stripline conductor and the ground plane.

R.F. connectors 51, 52 and 53 are electrically connected to tabs 12, 13 and 14, respectively, in substantially the same manner as those of FIGURE 3. Connector 53 is secured to one face of blocks 73 and 76 while connectors 51 and 52 are secured to the opposite face of these blocks. This construction is highly desirable because direct connections between the ground plane formed by blocks 73 and 76 and the connector ground portions is affectedand the stripline elements are effectively shielded.

It should now be apparent that there has been herein disclosed a new and novel directional coupler that is of small size and which requires no external termination. Units actually constructed for 1,100 megacycles, occupied slightly more than 10 cubic inches. Signals coupled from tab 14 to tabs 12 and 13 suffered virtually no attenuation while 20 db attenuation was maintained between tabs 12 and 13 over a 30 percent frequency band for center frequencies between 1,000 and 4,500 megacycles per second.

It is to be understood that the principles of the present invention may be utilized for isolation with coaxial cables, as Well as other types of transmission lines and phase shifters and are not limited to microwave frequencies.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

What I claim is:

1. A system for coupling energy in a predetermined microwave band with a center wavelength A between three coaxial conductors comprising an enclosure formed of a metal shield housing having a pair of planar, substantially parallel surfaces joined together by four walls, a dielectric board, means for maintaining said board in spaced parallel relation with said surfaces, said boardincluding strip line conductors on either side thereof, said strip line conductors being in registration, each of said strip line conductors comprising; a substantially circular portion, a pair of adjacent points on said portion being insulated, a sepa rate strip line tab connected to each of said adjacent points, a further strip line lead connected to said circular portion equidistant from said adjacent segments, the distance on said circular portion between said lead and each of said points being approximately M4, said strip line portions forming two 4 transmission lines having equal characteristic impedances; said board having a slot between said points, a resistor in said slot and being connected to said points, said resistor having an impedance equal to the characteristic impedance of one of said lines, a pair of coaxial connectors mounted in and extending through one of said walls, the inner conductor of each of said connectors being connected to one tab on each side of said board, the distances along said tabs between one of said points and one of said connectors and between the other of said points and the other one of said connectors being substantially equal, an additional coaxial connector mounted in and extending through another of said walls, said one and another walls being parallel, said leads on each side of said board being connected to the inner conductor of said additional connector.

2. The system of claim 1 wherein said housing comprises a pair of substantially U-shaped members having l their legs at right angles to each other, the legs of one of said members forming said surfaces, the legs of the other one of said members forming said parallel walls, the separation of said surfaces being less than the height of said parallel walls.

References Cited by the Examiner UNITED STATES PATENTS 2,614,170 10/52 Marie 333-11 v 8 2,803,750 8/57 'Dayem 333-10 2,874,276 2/59 Dukes 33384 2,969 510 1/61 White 33384 7 OTHER REFERENCES Stone: Microwave Multiplexing Circuits, Electronic Industries, vol. 17, November 1958, pages 62 to 65.

HERMAN KARL SAALBACH, Primary Examiner. 

1. A SYSTEM FOR COUPLING ENERGY IN A PREDETERMINED MICROWAVE BAND WITH A CENTER WAVELENGTH $ BETWEEN THREE COAXIAL CONDUCTORS COMPRISING AN ENCLOSURE FORMED OF A METAL SHIELD HOUSING HAVING A PAIR OF PLANAR, SUBSTANTAILLY PARALLEL SURFACES JOINED TOGETHER BY FOUR WALLS, A DIELECTRIC BOARD, MEANS FOR MAINTAINING SAID BOARD IN SPACED PARALLEL RELATION WITH SAID SURFACES, SAID BOARD INCLUDING STRIP LINE CONDUCTORS ON EITHER SIDE THEREOF, SAID STRIP LINE CONDUCTORS BEING IN REGISTRATION, EACH OF SAID STRIP LINE CONDUCTORS COMPRISING; A SUBSTANTAILLY CIRCULAR PORTION, A PAIR OF ADJACENT POINTS ON SAID PORTION BEING INSULATED, A SEPARATE STRIP LINE TAB CONNECTED TO EACH OF SAID ADJACENT POINT, A FURTHER STRIP LINE LEAD CONNECTED TO SAID CIRCULAR PORTION EQUIDISTANT FROM SAID ADJACENT SEGMENTS, THE DISTANCE ON SAID CIRCULAR PORTION BETWEEN SAID LEAD AND EACH OF SAID POINTS BEING APPROXIMATELY $/4 SAID STRIP LINE PORTIONS FORMING TWO $/4 TRANSMISSION LINES HAVING EQUAL CHARACTERISTIC IMPEDANCES; SAID BOARD HAVING A SLOT BETWEEN SAID POINTS, A RESISTOR IN SAID SLOT AND BEING CONNECTED TO SAID POINTS, SAID RESISTOR HAVING AN IMPEDANCE EQUAL TO THE CHARACTERISTIC IMPEDANCE OF ONE OF SAID LINES, A PAIR OF COAXIAL CONNECTORS MOUTED IN AND EXTENDING THROUGH ONE OF SAID WALLS, THE INNER CONDUCTOR OF EACH OF SAID CONNECTORS BEING CONNECTED TO ONE TAB ON EACH SIDE OF SAID BOARD, THE DISTANCES ALONG SAID TABS BETWEEN ONE OF SAID POINTS AND ONE OF SAID CONNECTORS AND BETWEEN THE OTHER OF SAID POINTS AND THE OTHER ONE OF SAID CONNECTORS BEING SUBSTANTIALLY EQUAL, AN ADDITIONAL COAXIAL CONNECTOR MOUNTED IN AND EXTENDING THROUGH ANOTHER OF SAID WALLS, SAID ONE AND ANOTHER WALLS BEING PARALLEL, SAID LEADS ONE EACH SIDE OF SAID BOARD BEING CONNECTED TO THE INNER CONDUCTOR OF SAID ADDITIONAL CONNECTOR. 